Chemical-mechanical polishing (CMP) may be utilized to remove material during the fabrication of semiconductor devices (e.g., integrated circuitry). An example CMP process is described with reference to FIG. 1. Specifically, a construction 10 comprises an upper structure 12 over a supporting base 14. The construction 10 is subjected to CMP to remove the upper structure 12, and to leave the base 14 with a planarized surface 15 thereover.
The structure 12 may comprise a single material, or may comprise multiple materials; and in some embodiments may be referred to as a mass, layer, etc.
The base 14 may be a semiconductor substrate. The term “semiconductor substrate” means any construction comprising semiconductive material (e.g., silicon, germanium, etc.), including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductor substrates described above. In some applications, the base 14 may correspond to a semiconductor substrate containing one or more materials associated with integrated circuit fabrication. Such materials may include, for example, one or more of refractory metal materials, barrier materials, diffusion materials, insulator materials, etc.
A difficulty which may occur during CMP is associated with determining an endpoint of the CMP process. Specifically, it may be desired to stop the CMP process quickly after the entirety of the upper structure 12 is removed, and before removing any significant amount of the base 14. If the base 14 comprises relatively hard material as compared to the upper structure 12, the endpoint of the CMP process may be ascertained by a change in friction. However, if the base 14 comprises soft material, it may be more difficult to ascertain the endpoint of the CMP process. Further, the soft material may be detrimentally deformed during the CMP process if too much pressure is applied to the soft material, resulting in dishing and/or other undesired attributes.
In some aspects, the base 14 may comprise a heterogeneous upper surface. For instance, FIG. 2 shows an example base 14 corresponding to a semiconductor wafer. A region of the surface 15 of base 14 is shown in expanded view, and such region includes multiple materials 16, 18 and 20. In some applications, the material 16 may be a relatively hard material (e.g., may comprise, consist essentially of, or consist of carbon), and the materials 18 and 20 may be relatively soft material. For instance, the material 18 may comprise silicon, oxygen and carbon; such as, for example, material deposited utilizing spin-on methodology. The material 20 may comprise, consist essentially of, or consist of silicon dioxide; and in some cases may correspond to low-density silicon dioxide. In some particular applications, the base 14 of FIG. 2 may correspond to a construction utilized during fabrication of three-dimensional cross-point integrated circuit architecture.
A difficulty in utilizing CMP to expose the upper surface 15 of the construction 10 of FIG. 2 is that the softer materials 18 and 20 may be deformed if too much pressure is utilized during the CMP and/or if the CMP is not stopped promptly upon reaching the desired endpoint (i.e., upon the initial exposure of upper surface 15). Accordingly, it would be desirable to develop improved methods of CMP.
A prior art CMP apparatus 30 is described with reference to FIGS. 3 and 3A. The apparatus 30 includes a platen (i.e., table) 32 coupled with a first shaft 34, and configured to spin (with the spinning being represented by an arrow 33). The apparatus also includes a wafer holder (i.e., carrier) 36, coupled with a second shaft 38, and configured to spin (with the spinning being represented by an arrow 35). Also, the wafer holder is configured to sweep laterally across an upper surface of the platen 32 (with the sweeping being represented with arrows 37). A wafer 10 is shown to be retained within the wafer holder 36. The wafer 10 has a surface 11 facing the platen 32, with such surface being polished during the polishing (i.e., CMP) process.
The movements of the platen 32 and wafer holder 36 are controlled utilizing a controller 40. Such controller may also control a downforce on the wafer holder 36 during a polishing process. The downforce is a vertical force on the wafer holder 36 which presses the wafer 10 toward an upper surface of the platen 32, and corresponds to a vertical force on the surface 11 of the wafer 10 during the polishing process.
The apparatus 30 includes a dispenser 40 which dispenses slurry 42 onto the platen 32. The dispenser 40 may be considered to be part of a slurry-dispensing mechanism, and is in fluid indication with a reservoir (not shown) containing the slurry.
The slurry 42 forms a film 44 across an upper surface of the platen 32, with such film extending to under the wafer 10. The slurry 42 is initially a fresh slurry as it is dispensed onto the upper surface of platen 32, but becomes a used slurry after it is utilized for polishing the surface 11 of wafer 10. The used slurry will carry materials removed from wafer 10. The used slurry is expelled outwardly through centrifugal force, with the outward movement of the slurry being indicated with arrows 43.
A shield 46 surrounds a lateral periphery of the platen 32, and is configured to block laterally expelled used slurry during the polishing process.
A basin 48 collects the used slurry. The basin 48 comprises outlets 50, and the slurry exits the basin through the outlets 50. The illustrated basin 48 is shown to comprise a pair of the outlets 50 along the cross-sectional view of FIG. 3. The basin may comprise more than two outlets in some applications, or may comprise only a single outlet.
In some applications, an endpoint of a CMP process is determined by a change in friction along the surface 11 of wafer 10 due to a change in the materials exposed along such surface. The change in friction may be detected by the controller 40 as a change in the power required to maintain a particular spinning rate of platen 32. The CMP apparatus 30 of FIGS. 3 and 3A may be effective in applications in which the endpoint of the CMP process may be determined by the change in friction.
In some applications, the endpoint of a CMP process cannot be readily determined simply by a change in friction along the surface 11 of wafer 10. For instance, if the downforce on wafer 10 is relatively light (i.e., less than or equal to about 1 pound per square inch (psi) during the polishing process), the change in friction may be difficult to detect. Further, a reason for utilizing a relatively light downforce is because a final polished surface of wafer 10 will comprise soft materials (with example soft materials being the silicon dioxide materials described above with reference to FIG. 2), and polishing beyond the desired endpoint may be particularly problematic relative to soft materials (as discussed above with reference to FIGS. 1 and 2). Accordingly, it would be desirable to develop improved apparatuses for utilization in CMP applications in which frictional changes are not suitable for determining the endpoint of a polishing process, and to develop improved methods for CMP.